In U.S. Pat. No. 4,239,338, Borrelli et al. teach an optical information storage medium comprising a glass substrate, a 100 Angstrom thick silver layer applied to the substrate, an oxide layer deposited over the silver layer and a multilayer additively colored AgCl/PbO film applied over the oxide layer. The film is optically bleachable using visible light to produce a dichroic, birefringent image. The image is read in infrared light, since the film is transparent at infrared wavelengths down to the silver layers. The silver layer permits reading and writing in the reflective mode. The film should have a thickness not exceeding about two microns to permit high spot resolution.
In U.S. Pat. No. 4,278,756, Bouldin et al. teach a reflective laser recording and data storage medium formed from a photosensitive silver-halide emulsion. The emulsion is exposed and developed using a negative silver diffusion transfer process to make the film surface shiny compared to data spots which are clear or dark. The shiny surface may be above or below the main body of the emulsion depending on whether the reading light is to be introduced from above or from below through a clear substrate.
In reflective optical data storage media, high optical contrast between data spots and the media background and sharply defined data spots are necessary for resolving data, particularly where data spots are small, i.e. one micron or less in size. For optical disks it is also desirable that the optical storage and recording media provide several capabilities in addition to high contrast and high resolution. The media should record with a laser beam, and it should be capable of prerecording servo track guides, timing marks or other formatting indicia and data during manufacturing, and it should be capable of laser recording formatting patterns and data on a finished memory disk. While optical cards are valuable with data bits as large as three to ten microns and optical tape is valuable with data bits as large as one to five microns, optical disks require data bits one micron or smaller to be valuable.
An object of this invention was to achieve adequate recording sensitivity for laser written data on reflective read optical storage media applicable to optical disks, while providing for optional pre-recording of track guides and other formatting information prior to completion of the finished disk and also providing for laser recording of data on finished optical disks.